Voltage Ranges and Settings
For testing functional limits, you can set custom voltage levels in 10 mV increments from –2 V to +5.5 V. This range allows compatibility with common logic families such as CMOS, TTL, and LVTTL, as well as custom logic levels. The Channel Electronics diagram shows how these voltage levels are used with the dual comparators and the variable voltage driver.
You can set four voltage levels on the NI 655x: Generation Voltage High and Low Levels and Acquisition Voltage High and Low Level. Generation voltage levels are the voltage levels used for all data, clock, and event generations, with the exception of the exported PLL reference clock, which is fixed at 3.3 V Logic. Acquisition voltage levels are used for all acquired data, clock, and trigger signals, except for the CLK IN SMB jack connector. Refer to Clock Sources Summary for acceptable CLK IN signal characteristics.
When programming your device using NI-HSDIO, the functions and instance VIs for configuring voltage levels are named according to the type of channel (data, trigger, or event) that you want to configure. For more information about configuring voltage levels with NI-HSDIO, refer to Configuring Voltage Levels.
To stay within PXI and PCI power and cooling requirements, the allowable generation voltage levels are reduced at higher Sample clock frequencies. The following table shows the relationship between Sample clock frequency and allowable generation voltage levels.
NI 655x Generation Voltage Level Limits
| Typical Application | Sample Clock Frequency | Minimum Level | Maximum Level |
|---|---|---|---|
| Negative logic | Up to 50 MHz | –2.0 V | 3.7 V |
| 5 V Logic | Up to 50 MHz | –0.5 V | 5.5 V |
| 3.3 V Logic | Up to 50 MHz (NI 6551) Up to 100 MHz (NI 6552) |
–0.5 V | 3.7 V |
You can independently set Generation Voltage High and Generation Voltage Low anywhere from the minimum level to the maximum level shown in the table, depending on your application and Sample clock frequency. Acquisition Voltage High and Acquisition Voltage Low can always be independently set anywhere between –2.0 and 5.5 V, regardless of the Sample clock frequency. By synchronizing and operating multiple NI 655x devices, you can use different voltage configurations in the same system.
For more information about voltage level ranges and resolutions, refer to NI 655x specifications.